Landscape Evolution Modelling with LAPSUS: Time step and stepping time

Abstract An important decision in Landscape Evolution Modelling is the timestep or dt in between each processing and calculation step. Officially the ‘Courant-Friedrichs-Lewy (CFL) criterion’ is a condition in solving numerical equations that states that, given a spatial resolution or discretization, a time step larger than some computable quantity should not be taken. This criterion is expected to be violated in LEM LAPSUS, a multi modular reduced complexity model, since annual or larger time-steps are chosen above ideal re-sedimentation budgets. However, processing only the sediment budgets that are allowed on one single cell \ that might slow down considerably computation speed in complex landscapes. In this LEM experiment we simulate the effect of changing the temporal resolution (time-step) on various landscapes, without changing any of the other LEM formulations or conditions. The sediment travel distance will decrease and sediment budgets smaller. Consequently model results tell us something on the stability of our model formulations and whether the above mentioned assumptions indeed justify the violation of the CLF criterion.